1. Field of the Invention
The invention relates to acrylate copolymer blends and in particular to ethylene methylacrylate copolymer/ethylene butylacrylate copolymer blends and their use as a layer or interlayer which is bonded to mineral (e.g., glass) or polymer substrates for the manufacture of bilayer or multiple layer laminates. In particular, these films are useful between two or more transparent layers made of glass or polymer materials for use as safety glass for automotive and architectural applications.
2. Technology Review
For over three decades significant efforts have been made to find an interlayer film which performs as well as polyvinylbutyral (PVB) without its inherent drawbacks. A number of polymers and formulations based on them have been used to produce transparent interlayer films for bilayer and multiple layer mineral (e.g., glass) or polymer sheets, particularly for flat glass products in automotive and architectural safety glass applications. The major glass laminate manufacturers for the most part have still found that for their cost polyvinylbutyral (PVB) compositions provide the best overall performance and therefore these have been the interlayer of choice for laminated glass applications.
The performance of the interlayer films is based on film characteristics such as tensile strength, elongation at break, softening point and glass adhesion strength and laminate properties such as luminous transmittance, boil test stability, humidity test stability, light stability and impact and penetration resistance. While conventional PVB interlayers perform well, they do suffer from several drawbacks.
The major drawback of PVB is its moisture sensitivity.
This is important because during storage and use under what would be considered typical conditions in a flat glass manufacturing environment there is the potential for significant increases in moisture content. The increased moisture in interlayer films results in increased haze and may cause bubble formation in the final laminated flat glass products which is unacceptable to both the manufacturers and their customers. Therefore, special precautions have to be taken to keep the moisture content of the PVB film and ulitmately the haze of the laminated flat glass products to an optimum. These special precautions may include reducing storage times of the PVB film to a minimum, refrigeration of the PVB film prior to lamination, pre-drying of the PVB film and/or the use of dehumidifiers in the clean rooms used for preparing the laminates. This both increases the cost and the difficulty in manufacturing laminates made with a polyvinyl butyral interlayer. Even then when the edges of the laminated glass are exposed to moisture, haze will develop.
Another drawback of PVB is the need for a plasticizer in film for bonding the PVB to the glass. The plasticizer tends to migrate over time leading to changes in the properties of the laminate and in particular delamination will begin to occur at the edges of the laminated glass due to loss of the plasticizer.
The other polymers and formulations which have been used or tried include those based on polyurethane (PU) polyvinylchloride (PVC), ethylene copolymers such as ethylenevinylacetate (EVA), polymeric fat acid polyamide (PAM), polyester resins such as polyethyleneterephtalate (PET), silicone elastomers (SEL), epoxy resins (ER) or polycarbonates such as elastomeric polycarbonates (PC and EPC). While many of these polymers and formulations do not have as relatively significant a moisture absorption problem as PVB, they do lack the overall performance of the PVB films at comparable costs. Further, some of these polymers and formulations require enhanced processing such as irradiation or the use of additional chemical components such as plasticizers which affect the cost and properties of the film and the flat glass products made using the film. For example, plasticizers will tend to migrate over time further affecting the properties of both the film and the products made using the film.
An object of this invention is to produce a polymer film which has a tensile strength, moisture absorption, elongation at break, softening point and a glass adhesion strength which are comparible or superior to PVB, and which can be incorporated in laminated glass products such as windshield and architectural safety glass that have a luminous transmittance, boil test stability, humidity test stability, light stability and impact and penetration resistance comparible or superior to those made with PVB.
A further object of this invention is to produce an ethylene acrylate copolymer blend and film which is useful as a component of optical laminates.
A further object of this invention is to produce an ethylene acrylate copolymer blend and film which can be processed into an interlayer under conditions similar to those used for processing PVB.
The present invention comprises a film formed from an acrylate blend. The preferred blend comprising components (a) and (b), component (a) being an ethylene butyl acrylate copolymer (EBAC) which is less than about 95 percent percent by weight of a total weight of components (a) and (b), wherein the EBAC has a content of acrylate groups from about 8 to about 36 percent by weight of the total weight of the EBAC; and component (b) being an ethylene methyl acrylate copolymer (EMAC) which is greater than about 5 percent by weight of the total weight of components (a) and (b), wherein the EMAC has a content of acrylate groups from about 8 to about 42 percent by weight of the total weight of the EMAC.
The invention further includes a process for manufacturing this film comprising the steps of mixing the melt of thermoplastic polymer resins to form an ethylene butyl acrylate/ethylene methyl acrylate blend and forming the ethylene butyl acrylate/ethylene methyl acrylate blend of thermoplastic resins into a film. The invention still further includes a laminate comprising at least a first layer which is typically transparent and at least one layer comprised of the film described above. The invention still further includes a laminate comprising an acrylate film laminated between two lamina wherein the film and the laminate have properties similar to PVB and laminates made with PVB, respectively.
The present invention is a film which has particular utility in glass laminates. The film comprises a blend of two or more acrylates. Examples of these acrylates include ethylene butyl acrylate, ethylene methyl acrylate, isobutylacrylate, and ethylene propyl acrylate. These examples are; however, given by way of illustration and not by way of limitation. The film, preferably, comprises a blend of two components. These being component (a) which is an ethylene butyl acrylate copolymer and component (b) which is an ethylene methyl acrylate copolymer.
The ethylene butyl acrylate (EBAC) of component (a) has a content of acrylate groups from about 8 to about 36 percent, preferably from about 16 to about 26 percent by weight and more preferably from about 18 to about 22 percent by weight of the total weight of the ethylene butyl acrylate (EBAC).
The ethylene methyl acrylate of component (b) has a content of acrylate groups from about 8 to about 42 percent, preferably from about 20 to about 32 percent, and more preferably from about 22 to about 27 percent by weight of the total weight of the ethylene methyl acrylate (EMAC).
The melt flow rate of the ethylene butyl acrylate copoylmer (EBAC) used as component (a) of the film as measured by ASTM Test Method D-1238 is preferably from about 0.5 to about 20.0 grams/10 minutes, more preferably is from about 0.5 to about 10 grams/10 minutes, and most preferably is from about 0.5 to about 6.0 grams/10 minutes.
The melt flow rate of the ethylene methyl acrylate copoylmer (EMAC) used as component (b) of the film as measured by ASTM Test Method D-1238 is preferably from about 0.5 to about 100.0 grams/10 minutes, more preferably is from about 0.5 to about 20 grams/10 minutes, and most preferably is from about 2.0 to about 6.0 grams/10 minutes.
The amount of component (a) present in the film is less than about 95 percent by weight of the total weight of components (a) and (b), and the amount of component (b) present in the film is greater than about 5 percent by weight of the total weight of components (a) and (b). Preferably, the amount of component (a) present in the film is from about 95 percent to about 1 percent by weight of the total weights of components (a) and (b), and the amount of component (b) present in the film is from about 5 percent to about 99 percent by weight of the total weights of components (a) and (b). Still preferably, the amount of component (a) is from about 95 percent to about 5 percent by weight of the total weight of components (a) and (b), and the amount of component (b) present in the film is from about 5 percent to about 95 percent by weight of the total weight of components (a) and (b). More preferably, the amount of component (a) is from about 50 percent to about 5 percent by weight of the total weight of components (a) and (b), and component (b) is from about 50 percent to about 95 percent by weight of the total weight of components (a) and (b), and more preferably component (a) is from about 20 percent to about 5 percent by weight of the total weight of components (a) and (b), and component (b) is from about 80 percent to about 95 percent by weight of the total weight of components (a) and (b).
The relative amounts of components (a) and (b) may be varied within the defined ranges in order to satisfy the needs of a particular application or process. Variation of the components further depends on other variables including for example the nature of the substrate or laminus (e.g., whether it is a polymer or a glass). Changes in the relative amounts of (a) and (b) lead to changes in properties including for example transparency, haze, tensile modulus, softening point and penetration resistance.
The film of the invention may employ one or more additives. All of the additives are designated in this specification as component (c). The additives include for example cross-linking agents, coupling agents, nucleation agents, UV-light absorbers, IR-light absorbers, pigments and other additives depending on the type and application of the final laminated product. This list of additives is by no means exhaustive and is therefore given by way of illustration and not by way of limitation.
Preferably, the amount of the additives as a group called component (c) present in the film may consist of from about 0.25 percent to about 15.0 percent by weight of the total weight of components (a), (b), and (c), more preferably is from about 0.5 percent to about 10.0 percent by weight of the total weight of components (a), (b), and (c), and most preferably is from about 1.0 percent to about 5.0 percent by weight of the total weight of components (a), (b), and (c).
Preferably, the film comprises a coupling agent and a clarifying agent known as components (c) (i) and (c) (ii), respectively; and more preferably the film further comprises a cross-linking agent known as component (c)(iii). Preferably, the amount of the coupling agent (c) (i) present in the film consists of from about 0.10 percent to about 6.0 percent by weight of the total weight of components (a), (b) and (c), the amount of clarifying agent (c) (ii) present in the film consists of from about 0.05 percent to about 3.0 percent by weight of the total weight of components (a), (b) and (c), and the amount of cross-linking agent present in the film consists of up to about 5.0 percent by weight of the total weight of components (a), (b) and (c). Still preferably, the amount of the coupling agent (c) (i) present in the film consists of from about 0.10 percent to about 4.0 percent by weight of the total weight of component (a), (b) and (c), the amount of clarifying agent (c) (ii) present in the film consists of from about 0.15 percent to about 3.0 percent by weight of the total weight of components (a), (b) and (c), and the amount of cross-linking agent present in the film consists of up to about 4.0 percent by weight of the total weight of components (a), (b) and (c). More preferably, the amount of the coupling agent (c) (i) present in the film consists of from about 0.20 percent to about 2.0 percent by weight of the total weight of component (a), (b) and (c), the amount of clarifying agent (c) (ii) present in the film consists of from about 0.50 percent to about 2.0 percent by weight of the total weight of components (a), (b) and (c), and the amount of cross-linking agent present in the film consists of up to about 3.5 percent by weight of the total weight of components (a), (b) and (c). Most preferably, the amount of the coupling agent (c) (i) present in the film consists of from about 0.20 percent to about 1.0 percent by weight of the total weight of component (a), (b) and (c), the amount of clarifying agent (c)(ii) present in the film consists of from about 0.50 percent to about 1.5 percent by weight of the total weight of components (a), (b) and (c), and the amount of cross-linking agent present in the film consists of from about 0.30 percent to about 2.5 percent by weight of the total weight of components (a), (b) and (c).
Cross-linking agents may be used to increase the softening point of the film. The preferred cross-linking agent is an organic peroxide, and is chosen from peroxides with appropriate kinetics of degradation to be stable enough during mixing of the formulation. This includes peroxide compounds preferably having at least a 10 hour half-life at decomposition temperatures greater than 70xc2x0 C., and more preferably only includes compounds having at least a 10 hour half-life at decomposition temperatures greater than 100xc2x0 C. The half-life of the organic peroxides is defined as the time in which half the chemical decomposes at the given temperature.
Examples of cross-linking agents which may be used include 2,5-dimethylhexane-2,5-dihydroperoxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3; di-t-butyl peroxide; t-butylcumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; dicumyl peroxide; a, axe2x80x2-bis (t-butylperoxyisopropyl)benzene; n-butyl-4,4xe2x80x2-bis(t-butylperoxy)valerate; 2,2-bis(t-butylperoxy)butane; 1,1-bis(t-butylperoxy)cyclohexane; 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane; t-butylperoxy benzoate; benzoyl peroxide; or combinations of these. The examples of peroxides are given by way of illustration and not by way of limitation. The more preferred cross-linking agent is dicumyl peroxide.
Cross-linking may also be accomplished by electron beam treatment of the film to increase the softening point. The electron beam intensity is preferably in the range of from about 2 to about 20 MRads for a time sufficient to increase the softening point to between about 110 to about 125xc2x0 C.
Coupling agents may be used to increase the bondability of the film to a lamina without pre-treatment of the surface of the lamina with primers. The preferred coupling agents are silane coupling agents. Examples of silane coupling agents which may be used include for example chloropropylmethoxysilane; vinyltrichlorosilane; vinyltriethoxysilane; vinyl-propyl trimethoxysilane; (3,4-ethoxycyclohexyl)ethyl-trimethoxysilane; glicidoxypropyl trimethoxysilane; vinyl-triacetoxysilane; aminopropyl triethoxysilane or combinations of these. The examples of coupling agents are given by way of illustration and not by way of limitation. The more preferred coupling agent is vinyltriethoxysilane.
Clarifying agents may be used to increase the transparency and decrease the haze of the film. The clarifying agents are nucleating agents which decrease the haze and increase the transparency of the film by decreasing the amount of crystallinity, and controlling the size and uniformity of the crystals in the film. The processing conditions (e.g., cooling rate) of the film can also affect the amount, size and uniformity of crystals in the film. The preferred clarifying agents are organic nucleators. Examples of organic nucleators which may be used include for example polyol acetals. The more preferred clarifying agents are polyol acetals sold under the tradenames Millad 3940 and manufactured by Milliken Chemicals of Spartanburg, S.C., and Mark 2180 manufactured by Witco Corporation, New York, N.Y.
UV and IR light absorbers may be used to provide the film and the laminated product with particular absorption and reflection characteristics, and pigments and other optical effect additives may be used to provide the film with special colors (e.g., shade band, etc),and other optical effects.
The film produced from these acrylate blends preferably has a tensile strength at break greater than about 13.0 N/mm2, more preferably greater than about 14.0 N/mm2, and most preferably greater than about 16.0 N/mm2. Preferably the elongation at break is greater than about 400 percent, more preferably greater than about 500 percent, and most preferably greater than about 700 percent. Preferably, the water content upon storage at 50 percent relative humidity at 50xc2x0 C. for 14 days is less than about 0.20 percent by weight, more preferably less than about 0.15 percent by weight, and most preferably less than about 0.10 percent. Preferably, the tear strength is greater than about 24.0 N/mm, more preferably greater than about 27.0 N/mm, and most preferably greater than about 30.0 N/mm. Preferably, the softening point is greater than about 80xc2x0 C., more preferably greater than 105xc2x0 C., and most preferably greater than about 115xc2x0 C.
The process for manufacturing the film of the invention comprises the steps of mixing and heating the thermoplastic polymer resins to form an acrylate blend or in the preferred embodiment an ethylene butyl acrylate/ethylene methyl acrylate blend, wherein the ethylene butyl acrylate/ethylene methyl acrylate blend of thermoplastic polymer resins comprises components (a) and (b) and optionally (c) as described above; and forming the ethylene butyl acrylate/ethylene methyl acrylate blend of thermoplastic resins into a film.
The processing of a film from Components (a), (b) and optionally (c) can be accomplished by mixing the components along with the application of heat. The mixing of the components and the application of heat can take place in any order including the mixing of the components before, during, or after the application of heat.
The processing temperatures required for mixing the blend and forming the film are affected by many factors including pressure, time at temperature, whether the heat is applied before, during or after mixing, and the degree of mixing. Depending on the processing technique used the blend can be formed into pellets or other shapes known to those skilled in the art for further processing or can be directly formed into the desired film.
The preferred method of processing comprises forming pellets or other shaped pieces by heating and mixing the components (a), (b) and optionally (c) simultaneously. The pellets or other shaped pieces may be formed into a film by for example extrusion, casting or blow-extrusion or other means for producing film known to those skilled in the art. Extrusion is the preferable method of forming the film, and if extrusion is used the extruder is preferably equipped with a flat or ring die. The film is preferably formed at temperatures from about 160xc2x0 C. to about 240xc2x0 C., more preferably at temperatures from about 170xc2x0 C. to about 230xc2x0 C., and most preferably from about 180xc2x0 C. to about 220xc2x0 C.
The formed film may be used as an interlayer in a laminate. Preferably, the laminate can be formed comprising at least two layers separated by at least one interlayer, wherein the interlayer is a film formed from components (a), (b) and optionally (c) described above.
The lamina or sheets used to form the laminate can be flat or bent. The lamina or sheets can be glass, glass-ceramic or polymers. Examples of polymers which may be used include polymethyl methacrylate and polycarbonate. These examples of polymers are given as an illustration and not as a limitation. The preferred glass would be a soda-lime-silicate glass which is commonly used in the flat glass industry. The interlayer is the film described above as a ethylene butyl acrylate/ethylene methyl acrylate blend with or without additives.
Generally, the laminate comprises at least one lamina laminated to a polymer interlayer, however, when the laminate comprises at least two lamina the laminate is formed comprising x number of sheets separated by x-1 number of layers of polymer interlayer wherein x is at least two. The sheets can be of any thickness, however, for the process of lamination it is preferred that the sheets are from about 0.25 to about 12.7 mm thick, more preferably from about 1.25 to about 5 mm thick, and most preferably from about 1.5 to about 3.5 mm thick. The sheets and the interlayer can be laminated together by processes known to those skilled in the art. An example of process used to mature the laminate is the use of an autoclave which is given by way of illustration and not by way of limitation.
Laminates made using this film are made from an acrylate blend and two lamina, wherein the film is laminated between the two lamina, and wherein the laminate has the following properties.
The laminate preferably has a luminous transmittance which is greater than about 82.0 percent, more preferably greater than about 85.0 percent, and most preferably greater than about 87.0 percent. Preferably, the laminate""s haze is less than about 1.0 percent, more preferably less than about 0.5 percent, and most preferably less than about 0.35 percent. Preferably, the peel strength is greater than about 15 N/cm, more preferably greater than about 20 N/cm, and most preferably greater than about 30 N/cm. Preferably, the laminate can further pass the standard German penetration test DIN 52338.